It is important for your reference materials to be both clear and dynamic. By clarity, I refer to the ability to discriminate between the many larger forms and their smaller component forms. Also you must be able to demonstrate for the understanding of the artist how they effect the motion, balance, action and function of the parts in relation to the whole.

When I say they must be dynamic, I mean they must not only dissect each part and not deal with their connection, function or balance. The living organism is held together and made convincing in it's representation by the artist only by understanding the kinetic relationship of the whole and it's parts together in operation.

It can be compared to using words to make a meaningful sentence. Words without proper syntax, order and accentuation can be incoherent. Just the same, the body parts individually drawn well will not make the image convincing if they are not pieced together properly and given certain accentuation that reflects the meaning or function of what is going on. This is especially relevant to studies of facial expression and the subtle emotions that they convey.